A standard chuck as described in U.S. Pat. No. 4,302,021 has a chuck body formed centered on a chuck axis with an annular array of outwardly directed teeth. A plurality of generally angularly equispaced and radially displaceable jaws on the body can be displaced toward and away from each other by means of a tightening sleeve that is rotatable on the chuck body about the axis. A coupling ratchet pawl is pivoted on this sleeve and has an end engageable with the teeth so as only to allow rotation of the sleeve and chuck relative to each other so as to move the jaws toward one another, while preventing opposite rotation so that it acts like a one-way coupling. A spring is braced between this pawl and the sleeve and urges the pawl into radial engagement with the teeth. A release ring can be rotated relative to the chuck body between a torque-transmitting position allowing the spring to press the end of the pawl against the teeth and a releasing position holding the end of the pawl out of engagement with these teeth.
Such a chuck is self tightening in that, once it is clamped to a tool or workpiece and the coupling is set in the torque-transmitting position, its parts can only rotate in the tightening direction. Thus the chuck cannot loosen and any angular forces in the tightening direction will be effective only to further tighten it.
In this arrangement the tightening sleeve is formed with guides in which the jaws are axially and radially shiftable and in fact has two parts that are axially fixed to each other. The release ring is provided at the rear end of the chuck.
Such a chuck is operated to release or dechuck a tool or workpiece by rotating the release ring in one direction so as to retract the ratchet pawl, and then rotating the tightening sleeve in the opposite direction. Thus the user must normally grip the chuck with both hands, one on the release ring and one on the tightening sleeve, so as to oppositely rotate them, while taking care to subsequently only rotate the tightening sleeve while holding the release ring. To lock the chuck after rotating the tightening sleeve in one direction it is necessary to oppositely rotate the release ring, an operation that once again takes two hands and then the tightening operation similarly requires two hands.
Such operation of the chuck is relatively clumsy and is not in any way intuitive. A user not familiar with the chuck might not be able to use it at all, or is likely to leave it in the uncoupled condition in which there is no self-tightening action. Furthermore the chuck must be made axially long to allow the user to get a good grip on the two oppositely rotated parts, with the result that the tool incorporating this chuck is excessively long and top heavy.